1. Field of the Invention
The present invention generally relates to a dielectric waveguide, and more particularly, to a nonradiative dielectric waveguide used for a millimeter-wave band region, and suitable for millimeter-wave integrated circuits, and also, to a method of manufacturing such a nonradiative dielectric waveguide.
2. Background of the Invention
FIG. 10 shows one example of the construction of a conventional nonradiative dielectric waveguide, which includes a pair of flat plate-like conductor electrodes 101 and 102 disposed generally parallel to each other, and a dielectric strip line 103 held between said conductor electrodes 101 and 102 as shown. The dielectric strip line 103 is formed by a dielectric material such as a resin, ceramics or the like, into approximately a cubic rectangular configuration having a cross section, for example, with a width "b" and a height "c" each of several millimeters in length.
When a distance between the conductor electrodes 101 and 102 is represented by "a", and the wavelength of millimeter wave to be transmitted, in represented by .lambda., at a portion without the dielectric strip line 103, propagation of polarized waves parallel to the conductor electrodes 101 and 102 is cut off between said conductor electrodes, if the distance "a" is in a relation a &lt;.lambda./2. Meanwhile, at a portion where the dielectric strip line 103 is inserted, the cut off state is eliminated, and the electro-magnetic waves are propagated along the dielectric strip line 103. It is to be noted here that the transmission mode may be broadly divided into LSE mode and LSM mode, and in the LSE.sub.01 mode and LSM.sub.01 mode for the lowest order modes, LSM.sub.01 mode is normally employed from the viewpoint of low loss.
Incidentally, since the width b of the dielectric strip line 103 is small, it is not easy to bond said dielectric strip line 103 to the conductor electrodes 101 and 102. Thus, an effective means for securing the dielectric strip line 103 to the flat conductor electrodes 101 and 102 has not been available. Furthermore, in the case where the dielectric strip line 103 is made of a dielectric material such as Teflon resin or the like, it is particularly difficult to effect bonding. On the other hand, there may be considered a case where circuit components such as a circulator, an isolator, etc. are disposed between the conductor electrodes 101 and 102 to form an integrated circuit together with the conductor electrodes 101 and 102, and the dielectric strip line 103. In such a case, the circuit components can be more easily inserted between the conductor electrodes 101 and 102 when the conductor electrodes 101 and 102 and the dielectric strip line 103 are separated rather than when they are fixed together. Accordingly, in the nonradiative dielectric waveguide referred to above, it is so arranged that the conductor electrodes 101 and 102 and the dielectric strip line 103 are left separated from each other, and the dielectric strip line 103 is placed at a proper position on one conductor electrode 101 and conductor electrode 102 is placed on said dielectric strip line 103, thereby holding the dielectric strip line 103 between said conductor electrodes 101 and 102.
However, in the nonradiative dielectric waveguide described so far with reference to FIG. 10, positioning of the dielectric strip line 103 can not be readily effected, since the dielectric strip line 103 tends to move on the conductor electrode 101. If an integrated circuit is included, positioning of the dielectric strip line 103 itself must be accomplished, as well as the positioning between said dielectric strip line 103 and the circuit components is also required, and such positionings can not be readily effected. Accordingly, there has also been another problem related to low productivity, since the positioning as described above and positioning for properly holding the dielectric strip line 103 between the conductor electrodes 101 and 102 must be repeated many times in order to achieve desired characteristics. Moreover, even when the positioning of the dielectric strip line 103 is properly effected to provide the desired characteristics, deviation in the position of the dielectric strip line 103 tends to readily take place by mechanical vibrations, impacts, etc., since said dielectric strip line 103 is merely held by the conductor electrodes 101 and 102, and thus, there is also a problem that initial characteristics can not be fully maintained, thus lacking in reliability.
Moreover, since the conductor electrodes 101 and 102 are not connected with the dielectric strip line 103, there are cases where so-called side gaps are undesirably formed between the conductor electrode 101 and the strip line 103, and also, between the strip line 103 and conductor electrode 102.
FIG. 11 is a graphical diagram showing .omega.-.beta./k0 curves in the case where the side gaps are formed in the nonradiative dielectric waveguide in FIG. 10. It is to be noted that in FIG. 11, .omega. represents an angular frequency (Frequency f=.omega./2.pi.), .beta. denotes a phase constant, and k0 indicates wave number in a vacuum, and that .beta./k0 is equal to a ratio of a wavelength in a vacuum to the guide wave length, and the square thereof may be regarded as a relative effective dielectric constant. In the relation .beta./k0=1, the guide wave length is equal to the wavelength in a vacuum, and in the relation .beta./k0&gt;1, the guide wavelength becomes shorter then the wavelength in a vacuum, while in the relation .beta./k0&lt;1, the guide wavelength becomes longer than the wavelength in a vacuum.
The curve designated .phi.0 shows that the .omega.-.beta./k0 curve of the LSM.sub.01 mode at the side gap d=0. Meanwhile, the curves designated .phi.1, .phi.2, and .phi.3 respectively show the .omega.-.beta./k0 curves at the LSM.sub.01 mode in cases where the side gap d=0.01 mm, side gap d=0.05 mm, and side gap d=0.1 mm take place. In the LSM.sub.01 mode, since the electric field is weak in the vicinity of the side gap d, and is parallel to the conductor electrodes 101 and 102, energy accumulated at the side gap d is not so large. Therefore, in the LSM.sub.01 mode, the .omega.-.beta./k0 curve is shifted towards the higher frequency side as the side gap d becomes larger. On the other hand, the .omega.-.beta./k0 curve of LSE.sub.01 mode at the side gap d=0 is shown in .psi.0. Also, the .omega.-.beta./k0 curves at the LSE.sub.01 mode when the side gap d=0.01 mm, side gap d=0.05 mm, and the side gap d=0.1 mm are produced, and are respectively represented by .psi.1, .psi.2 and .psi.3. In LSE.sub.01 mode, since the electric field is strong near the side gap d, and the electric field is perpendicular to the conductor electrodes 101 and 102, the energy accumulated at the side gap d is large. Accordingly, in the LSE.sub.01 mode, inclination of the .omega.-.beta./k0 curve becomes smaller as the side gap d is increased. Therefore, when the side gap d is produced, the phase constants of the LSM.sub.01 mode and the LSE.sub.01 mode become undesirably close to each other (see .chi. in FIG. 11). Originally, the LSM.sub.01 mode and the LSE.sub.01 mode intersect at right angles to each other, without forming any mode coupling, but coupling is produced due to an asymmetrical nature by working errors. However, almost no coupling is produced if the difference in the phase constants is large, whereas conversely, the coupling tends to be readily produced if the difference in the phase constants is small. In other words, mode coupling tends to be formed since the phase constants of the LSM.sub.01 mode and the LSE.sub.01 mode come close to each other, with the consequence of an increase in transmission loss and the deterioration of transmission characteristics.
FIG. 12 shows the construction of another conventional nonradiative dielectric waveguide as disclosed in Japanese Patent Publication Tokkohei No. 1-51202. When a material with a high dielectric constant is employed for the dielectric strip line 103, the guide wave length .lambda.g becomes short. Thus, the length of the dielectric strip line 103 may be reduced for compact size of the nonradiative dielectric waveguide or integrated circuit, but on the contrary, the single operating range will become narrow due to generation of a new higher order mode. Moreover, variation of the characteristics due to the side gaps d between the conductor electrodes 101 and 102 and the dielectric strip line 103 tend to appear conspicuously. Therefore, in the nonradiative dielectric waveguide of FIG. 12, a high dielectric constant material is used for the dielectric strip line 103, and dielectric layers 105 are formed into flat plate-like shapes of a dielectric material having a dielectric constant lower than that of the strip line 103. Dielectric layers 105 are interposed between the dielectric strip line 103 and the conductor layers 101 and 102, whereby the single operating region is enlarged, while the variation of characteristics by the side gap is reduced. Furthermore, in the nonradiative dielectric waveguide of FIG. 12, as described so far, since the area for the dielectric layers 105 is large, there is a large bonding area between the conductive electrodes 101 and 102 and the dielectric layers 105, so that they can be readily bonded to each other so as not to be easily separated. Accordingly, the problems related to the positional deviation or side gaps between the conductor electrodes 101 and 102 and the dielectric layers 105 may be advantageously solved.
However, in the known nonradiative dielectric waveguide in FIG. 12, since the dielectric strip line 103 and the dielectric layers 105 are separately formed by different dielectric materials, it is not easy to bond the dielectric strip line 103 to the dielectric layers 105, and therefore, it is difficult to hold the dielectric strip line 103 between the dielectric layers 105. Accordingly, in this nonradiative dielectric waveguide, problems similar to those in the nonradiative dielectric waveguide of FIG. 10 also occur, i.e., problems of productivity, reliability and transmission characteristics.
FIG. 13 shows the construction of still another conventional nonradiative dielectric waveguide. In order to solve the problems related to the productivity and reliability in the known nonradiative dielectric waveguides described so far with reference to FIGS. 10 and 12, the nonradiative dielectric waveguide in FIG. 13 is formed with grooves 104 with a depth d for receiving the dielectric strip line 103 at predetermined corresponding positions of the conductor electrodes 101 and 102. Therefore, since the dielectric strip line 103 is properly positioned by merely fitting said strip line 103 into said grooves 104 without any particular consideration for the positioning thereof, assembling of the waveguide may be simplified for improvement of productivity. Moreover, although the strip line 103 is only held between the conductor electrodes 101 and 102, there is no possibility of positional deviation by mechanical vibrations and impacts, etc., since the strip line 103 is fitted in the grooves 104, and thus, initial characteristics of the waveguide may be maintained for higher reliability.
However, in the nonradiative dielectric waveguide in FIG. 13, there is another problem, and that is that high frequency current tends to concentrate upon corner portions .xi. of the grooves 104 by the characteristics of the high frequency wave, thus resulting in an increase of transmission loss. Moreover, the problem related to the deterioration of the transmission characteristics attributable to the mode coupling has not been solved in the waveguide of FIG. 13. FIG. 14 is a graphical diagram showing .omega.-.beta./k0 curves for the nonradiative dielectric waveguide of FIG. 13. In FIG. 14, .PHI.0 represents the .omega.-.beta./k0 curve for the LSM.sub.01 mode at the groove depth d=0, while .phi.1 shows the .omega.-.beta./k0 curve for the LSM.sub.01 mode at the groove depth d=0.2 mm. Thus, it is observed that, in the LSM.sub.01 mode, even when the groove depth d is increased, the .omega.-.beta./k0 curve is only slightly shifted towards the lower side of the frequency. Meanwhile, .psi.0 shows the .omega.-.beta./k0 curve in the LSE.sub.01 mode at the groove depth d=0, while .psi.1 represents the .omega.-.beta./k0 curve in the LSE.sub.01 mode at the groove depth=0.2 mm. In this case, it is seen that the .omega.-.beta./k0 curve is shifted to the higher side of frequency as the depth d of the groove increases. Accordingly, the .omega.-.beta./k0 curves for the LSM.sub.01 mode and the LSE.sub.01 mode approach each other to be finally overlapped (see .chi. in FIG. 14). In other words, since the phase constants for the LSM.sub.01 mode and the LSE.sub.01 mode are close to each other, there is still the problem of mode coupling resulting in an increase in transmission a deterioration of transmission characteristics.
FIG. 15 shows a construction of the further known nonradiative dielectric waveguide, which is disclosed in Japanese Patent Laid-Open Publication Tokkaihei No. 3-270401. The nonradiative dielectric in FIG. 15 includes a dielectric unit 107 and conductor electrodes 101 and 102 in order to solve the reliability problem resulting from positional deviation, and the problem of deterioration of transmission characteristics resulting from mode coupling. The dielectric unit 107 includes a dielectric strip line 103 disposed at a predetermined position, and having a vertical height H in a longitudinal direction and set to be smaller than half a wavelength, and planar portions 106 integrally formed with the strip line 103 and extending laterally in the left and right direction from the upper and lower edges of said strip line 103 so as to form an H-shaped cross section. The conductive electrodes 101 and 102 are formed in close contact on the outer surfaces of the planar portions 106, as shown.
In the nonradiative dielectric waveguide of FIG. 15, since the contact area between the dielectric strip line 103, planar portions 106 and conductor electrodes 101 and 102 are sufficiently large for close contact, there is no possibility that the dielectric strip line 103 and the planar portions 106 are separated from the conductor electrodes 101 and 102. Furthermore, since the dielectric strip line 103 is disposed at the predetermined position, it is not necessary to pay particular attention to the positioning of the strip line 103, or to the positional deviation thereof due to mechanical vibrations and impacts, and thus, it becomes possible to improve the productivity and reliability.
Moreover, there is no possibility that a side gap is produced between the conductor electrodes 101 and 102 and the dielectric strip line 103.
FIG. 16 is a graphical diagram showing .omega.-.beta./k0 curves for the nonradiative dielectric waveguide of FIG. 15. In FIG. 16, .phi.0 represents the .omega.-.beta./k0 curve for the LSM.sub.01 mode when the planar portion 106 is of thickness e=0. Meanwhile, .phi.1, .phi.2 and .phi.3 respectively show the .omega.-.beta./k0 curves for the LSM.sub.01 mode when the planar portion 106 is of thicknesses e=0.1 mm, e=0.2 mm, and e=0.3 mm, whereby it is seen that in the LSM.sub.01 mode, the .omega.-.beta./k0 curves are shifted towards the lower frequency as the thickness of the flange portion 106 increases. On the other hand, .psi.0 represents the .omega.-.beta./k0 curve in the LSE.sub.01 mode when the planar portion 106 in of thickness e=0, while .psi.1, .psi.2 and .psi.3 respectively show the .omega.-.beta./k0 curves in the LSE.sub.01 mode when the planar portion 106 is of thicknesses e=0.1 mm, e=0.2 mm and e=0.3 mm, whereby it is seen that in the LSE.sub.01 mode, the .omega.-.beta./k0 curves are only slightly shifted towards the lower frequency even when the thickness e of the planar portion 106 is increased. However, since the .omega.-.beta./k0 curves for LSM.sub.01 mode and LSE.sub.01 mode are sufficiently spaced apart, no mode coupling or transmission loss is produced to provide a stable performance as the transmission waveguide, and thus, the problem related to the transmission characteristics resulting from the side gaps may be advantageously solved.
However, in the conventional nonradiative dielectric waveguide as shown in FIG. 15, in the case where a circuit component is to be inserted between the conductor electrodes 101 and 102, the mounting of such a component therebetween is not easily done, since the dielectric strip line 103 and the planar portion 106 are fixedly bonded to each other, and thus, there is the problem that this arrangement is not suitable for formation with an integrated circuit.
In short, in the conventional nonradiative dielectric waveguides, there is either a problem relating to productivity, reliability or transmission characteristics.